I think they can grow into June if conditions are right...
<u>When is the growing season in my region?
This will depend on your geographical location. The morel season for most of the United States typically runs from early-to-mid April on through mid-June. Depending on your geographical location, your season could be plus or minus a week. The season will typically kick in about mid-April in the Great Lakes region. If one is uncertain, contacting your state's nature and wildlife department for assistance is a good idea if you can't find anyone to assist you. You can also check out The Great Morel's sighting maps to see if they are popping in your neck of the woods. The sightings map is a pretty good reference to the season for the various regions of the US.